1. Field of the Invention
This invention relates to a camera adapted for films provided with magnetic storage portions and, in particular, to an improvement of information writing to the magnetic storage portion.
2. Related Background Art
Conventionally, U.S. Pat. No. 4,977,419 discloses a color negative film including a virtually transparent magnetic layer on a base surface of the film, and a camera having a magnetic head for magnetically recording information in the film or for reading the information recorded in the film. It also discloses to provide on an outside edge of the exposed face of the film a plurality of recording tracks in which the camera records information magnetically. This increases the amount of information to be recorded for individual frames by means of increasing the number of recording tracks.
Disclosed as the information recordable by the camera is photographing information such as the date of photographing, time, the type of illumination light source used upon photographing, pseudo zoom information, exposing time, diaphragm values or the like.
Alternatively, U.S. Pat. No. 4,878,075 discloses that a filmstrip is previously provided with film information written therein such as film sensitivity and film regulated frame number, and that a camera reads this information before exposure while it re-writes this information upon taking up the film after completion of exposure to record various types of information upon photographing.
To read film information previously written in a magnetic layer on a base side of the film or to write photographing information in the magnetic layer in cooperation with an exposing operation by using a magnetic head disposed in a camera, the film is required to be transported with the magnetic head being joined to the above mentioned magnetic layer. With this respect, typical cameras are so structured that a film is pinched by spring operation between the magnetic head disposed on the base side of the film and a pad disposed at a position opposing to said magnetic head on the emulsion-applied surface of the film. Accordingly, flaws or pressure marks (sensitizing due to pressure) are caused on sliding portions to the magnetic head because of the pressure required for pinching. As a result, reading of the film information and writing of the photographing data by the camera are made only at the peripheries of frames out of the frames of the film.
FIGS. 6 and 7 are views for use describing the above. FIG. 6 is a view illustrating operation of magnetic recording on the film. In FIG. 6, F represents a film including a magnetic film (hereinafter, simply referred to as a film), F1 and F2 represent exposed frames, F3 represents an unexposed frame and P represents a perforation. T0 represents a film information track previously magnetically recorded in the film F, in which film information such as an ISO sensitivity of the film is recorded. A reference numeral 101 represents a magnetic head of a camera. The magnetic head comprises a first magnetic track forming unit 102 and a second magnetic track forming unit 103. T1 and T2 represent first and second photographing information tracks, respectively, for individual frames recorded by the first and the second track forming units 102 and 103 in place of the film information in the film information track T0 (overwriting using saturation recording) before one frame of the film is transported in a direction depicted by an arrow A.
FIG. 7 is a vertical sectional view of a camera having the above mentioned magnetic head 101. A reference numeral 111 represents a camera body provided with a well-known aperture opening 111a, a pair of upper and lower outer rails 111b, 111b, and a pair of upper and lower inner rails 111c, 111c. A reference numeral 112 represents a platen abutted to the outer rail 111b. The frame F travels through or stopped for exposure at a space (tunnel) defined by the outer rail 111b, the inner rail 111c and the platen 112.
The magnetic head 101 is secured to the platen 112 through a mounting plate 104 attached thereto and a vis 105. The first and the second track forming arrangements 102 and 103 are located at a position sliding with the film F from a notch 112a of the platen 112. In addition, the track forming arrangements 102 and 103 are laid out at a position outside the frame (depicted by C in the figure) by a photographing lens L. A reference numeral 113 represents a pad of an elastic material. The pad is secured to a receiving member 114a of a lever 114. The lever 114 comprises elongated bores 114b and 114c. Pins 115 and 116 are inserted into the elongated bores 114b and 114c, respectively. The pins 115 and 116 are fixed to the camera body 111. In addition, the lever 114 is forced rightward in the figure by a spring 117. The spring force of the spring 117 and the pad 113 forces the traveling film F continuously to the first and second track forming arrangements 102 and 103 of the magnetic head 101. (In FIG. 7, illustrated is a condition where the first and the second track forming arrangements are before forced.)
In this event, an alternating current adapted to a signal to be recorded flows through the first and the second track forming arrangements 102 and 103 to conduct magnetic recording. A magnetic field H generated in the track forming arrangements 102 and 103 are given by H.varies.T.times.A, where T represents the number of windings of a coil of the track forming arrangement while A represents a current value flowing through the coil. The magnetic field H to be required depends on the coercively of a medium subjected to the magnetic recording (the magnetic storage layer of the film F in this specification). A recording energy (i.e., the magnetic field generated at the track forming arrangement; the number of windings of the coil is involved in the direct current resistance, so that to increase H.varies.T.times.A corresponds to a power increase with respect to the device) applied by the device (the camera in this specification) to each track forming arrangement is normally constant. In view of reducing the energy for the device, the smaller recording energy is preferable as long as the coercive force of the medium can be withdrawn.
However, the above mentioned prior art has a disadvantage that the magnetic recording may be incomplete in the photographing information track (corresponding to T1 in FIG. 6) at the transversal end of the film. This is because the film end is curled in the direction away from the magnetic head 101 as depicted by FC in FIG. 7. Contact between the track forming arrangements 102, 103 and the film F is maintained by the spring 117 and the pad 113. However, the curling force is slightly larger than the spring force and the pad 113 is insufficient for forcing the film. As a result, a small gap (depicted by S in FIG. 7) is generated at the position of the track forming arrangement 102 close to the film end. This spacing loss is mainly responsible for the incomplete magnetic recording.
In addition, as shown in right-hand portion of FIG. 7, the above mentioned problem may be solved by means of attaching the magnetic head 101 to the platen 112 inclined by an angle .theta. to the direction along the curling of the film, which is still not a complete solution to the above problem.